FIG. 1 schematically shows the construction of a general cathode ray tube. As shown in the drawing, a panel 12 and a funnel 13 are formed integral to constitute a cathode ray tube 11. The inner space of these panel 12 and funnel 13 is held at a high vacuum. In order to allow the cathode ray tube to maintain a high resistance to implosion, a reinforcing metal band 14, which is called an explosion-proof band, is wound about the outer circumferential surface of the panel 12, with a Braun tube-holding metal tool 14a interposed therebetween, such that the panel 12 is fastened by the band 14. Also, the outer wall of the funnel 13 is coated with dag 15 consisting of an organic conductive material layer in order to obtain an electrical conductivity on the surface.
Further, an anti-reflection film of a multi-layer structure (not shown) is formed on the face 12a of the panel 12. A Braun tube equipped with an anti-reflection film, which serves to suppress reflection of the outer light, is used in recent years in mainly color TV receivers, terminal apparatuses of an electronic computer, etc.
Various methods such as a spinning method, a spraying method, a sputtering method and a vapor deposition method have been tried to date in an attempt to form a multi-layered anti-reflection film 16 on the face 12a of the panel 12. However, these methods have been found advantageous in some aspects and defective in other aspects. For example, the wet spinning method and spraying method permit forming the anti-reflection film at a relatively low cost and are suitable for mass production. However, the film is rendered thick, resulting in failure to obtain a desired reflectance.
On the other hand, a dry sputtering method or vapor deposition method permits forming a thin film, however, a large vacuum apparatus and, in some cases, a heating device are required, leading to a marked increase in the facility cost. Also, since a thin film is formed under vacuum in these methods, the atmosphere around a thin film-forming region must be discharged to establish a desired vacuum state, in this case, it takes a long time to establish the desired vacuum state, resulting in failure to improve the productivity.
FIG. 2 schematically shows a thin film-forming apparatus using a conventional sputtering method. As shown in the drawing, the apparatus comprises a vacuum chamber 18. The cathode ray tube 11 on which a thin film is to be formed is arranged within the vacuum chamber 18. A target 19 made of a desired material of the thin film is also arranged within the vacuum chamber 18 to face the cathode ray tube 11. The target 19 is disposed on a support member 20 which also acts as a cooling water pipe.
Each of the support member 20 and an annular body 21 arranged to surround the panel 12 of the cathode ray tube 11 is connected to a high frequency power source device or a DC power source device 22. Also, a magnet 23 is mounted to the support member 20 positioned behind the target 19. In this apparatus, a free space in which a magnetic field and an electric field intersect each other at right angles is formed by the magnet 23 and the DC power source device 22 in front of the surface of the target 19. An inert gas is introduced into the particular free space and a voltage is applied to the inert gas so as to bring about discharge.
A plasma 24 of a high density is generated by the discharge. It should be noted that a large amount of ions within the plasma 24 are accelerated by a bias voltage generated in the vicinity of the target 19 so as to bombard the target 19. As a result, atoms forming the target material are ejected from the target 19. In other words, a sputtering phenomenon takes place. The ejected atoms are deposited on the face 12a of the panel 12 of the cathode ray tube 11 positioned apart from the target 19 so as to form a thin film on the face 12a acting as a workpiece of the panel 12.
Where, for example, the target 19 is formed of zirconium oxide (ZrO.sub.2) and sputtering is performed under an argon gas (Ar) atmosphere, a thin film of zirconium oxide is formed on the face 12a of the cathode ray tube 11. Then, the material of the target 19 is changed into silicon, and sputtering is carried out under a mixed gas atmosphere consisting of an argon gas and an oxygen gas (O.sub.2) so as to form a thin film of silicon dioxide (SiO.sub.2) on the zirconium oxide thin film. In this fashion, different layers collectively forming the anti-reflection film 16 are successively formed on the face 12a of the panel 12, with the result that the face 12a is enabled to exhibit a desired reflectance.
In the conventional method of forming a thin film, however, the entire cathode ray tube 11 is disposed within the vacuum chamber 18 for forming the thin film. Naturally, the vacuum chamber 18 is required to have a large inner volume. Also, it takes much time to establish a vacuum state within the vacuum chamber 18, leading to a low efficiency. It should be noted that the high vacuum within the vacuum chamber 18 is broken every time the cathode ray tube 11 is put into and taken out of the vacuum chamber 18. In other words, the vacuum chamber 18 must be evacuated frequently. It follows that the evacuation to produce a vacuum condition within the vacuum chamber 18 takes much time, leading to a low productivity.
The outer surface of the funnel 13 except the face 12a of the panel 12 of the cathode ray tube 11 is coated with the organic conductive material layer 15. Where the cathode ray tube 11 is used as an electron tube under an ordinary condition, the organic conductive material layer 15 functions for ensuring an electrical conductivity on the surface and, thus, is useful. However, several problems are generated by the organic conductive material layer 15 where the cathode ray tube 11 is disposed under a vacuum environment. First of all, since a gas is contained in the organic conductive material layer 15, it takes a longer time for evacuating the vacuum chamber 18.
For shortening the evacuating time, it is conceivable to heat, for example, the cathode ray tube 11. If the cathode ray tube 11 is heated, however, a new problem is brought about that the organic conductive material layer 15 tends to peel off. The organic conductive material layer 15 peeling off the outer surface of the funnel 13 is accumulated within the vacuum chamber 18 and scattered in the evacuating step so as to be attached to the face 12a of the panel 12 of the cathode ray tube 11. It follows that the product cathode ray tube 11 is rendered defective.
Further, as described previously, the band 14 is wound about the panel 12 for fastening the panel 12 in order to allow the cathode ray tube 11 to maintain a high resistance to implosion. It should be noted in this connection that, if the cathode ray tube 11 is put in the vacuum chamber 18 held at a high vacuum, the pressure difference between the outer space and the inner space of the cathode ray tube 11 is diminished, with the result that the cathode ray tube 11 tends to be swollen and the band 14 is pushed radially outward. Then, if the cathode ray tube 11 is taken out of the vacuum chamber 18, the cathode ray tube 11 is caused to shrink by the atmospheric pressure, leading to a weakened fastening force of the band 14. It follows that the cathode ray tube 11 tends to fail to exhibit a sufficient resistance to implosion.